# Trig

the center of a circle
x^2 + y^2 + 8y =1 is
a. (0,-2)
b. (0,4)
c. (0,1)
d. (0,-4)
I believe the answer is (0,4)
Am I correct ?

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1. Incorrect!

you have to complete the square to get it into standard form

x^2 + y^2 + 8y + 16 = 1 + 16
x^2 + (y+4)^2 = 17

Now what do you know from your previous posts on this?

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2. I'm not sure what your looking for Reiny. It looks like the center of the circle is still (0,4) what am I doing wrong?

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3. (x+0)^2 + (y+4)^2 = 17
the center would be (0,4)
I can't see it any other way ...arghhhh

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4. I pointed out the pattern for you in
http://www.jiskha.com/display.cgi?id=1325732520
and you seem to be able to understand in your posts that follow it,
Now suddenly you have it backwards again.

remember that the sign is opposite what you see in the brackets
so for (x-5)^2 + (y+7)^2 = 100
the centre would be (+5, -7)

so for the above question is would obviously be
(0, -4)

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5. ARGHHHHH now that really was a brain on my part ...
Thanks a lot Reiny for the help
Don

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